An optical pulse test device called an optical time domain reflect meter (OTDR) has generally been used in the prior art to detect a defect, etc. of an optical fiber used as a communication cable, etc.
FIG. 8 shows a structure of a conventional optical time domain reflect meter (OTDR) 10 for testing the optical fiber, as described above.
The optical time domain reflect meter (OTDR) 10 comprises a light pulse generator 11 for outputting pulse-like light, a light receiver 12, and an optical coupler 14 for guiding a light pulse output from the light pulse generator 11 to an optical fiber 1 to be tested via an optical connector 13 and also guiding to the receiver 12 the light (backward scattering light or Fresnel reflection light) returning from the optical fiber 1 toward the optical connector 13.
In the optical time domain reflect meter (OTDR) 10, an output signal from the light receiver 12, which has been obtained in a predetermined time period since the light pulse was output from the light pulse generator 11, is processed to generate a measurement signal corresponding to transmission characteristics of the optical fiber 1 in the distance direction of the fiber. A waveform level of the measurement signal is plotted on a time axis (a distance axis) on a monitor screen.
The user compares the waveform displayed on the monitor screen and a waveform measured in advance when the optical fiber was laid out and thus finds a position on the optical fiber where abnormality has occurred. Thus, the defect of the optical fiber is detected and repaired.
In the above-described conventional optical time domain reflect meter (OTDR) 10, however, the user is unable to distinguish a loss increased due to only abnormality on the optical fiber side from a signal level variation on the OTDR body side due to a change in ambience, for example, a drift due to characteristics of the OTDR itself, such as a signal level variation resulting from an output variation of the pulse generator or an amplification degree variation of the light receiver. Consequently, the user may erroneously determine a defect of the optical fiber.
Besides, in the above-described optical time domain reflect meter (OTDR), the user compares the waveform displayed on the monitor screen and a waveform measured in advance when the optical fiber was laid out and thus finds a position on the optical fiber where abnormality has occurred. Thus, the defect of the optical fiber is detected. With this optical time domain reflect meter (OTDR) alone, it is not possible to perform an automatic monitor operation aiming at detecting a defect, etc. of the optical fiber.